Field of the Invention
Embodiments of the present invention relate, in general, to composite vehicle structures and more particularly to the productions and design of a composite vehicle frame having an internal support structure.
Relevant Background
Land vehicles have traditionally been designed to utilize a steel rail frame for support. This frame includes cross-connecting components to add rigidity and strength and it is this frame that serves as the foundation around which the rest of the vehicle is designed. As one skilled in the mechanical arts will appreciate, a substantially parallel rail frame design requires cross members to enhance the structures rigidity and strength. Unfortunately, the cross members also increase the vehicle's air resistance, weight and the cost of manufacture. As is well known to one skilled in the relevant art, most vehicle frames are steel. Steel is not the strongest, cheapest or lightest material. While other materials such as aluminum or titanium could be used to construct a frame, the selection of steel has traditionally been used for its ability to provide a strong platform which can be reliably fabricated and produced at an acceptable weight and reasonable cost. Re-examination of these parameters has generally been of little concern.
While weight versus strength has always been one aspect of land vehicle design, it has held a less important role than with the design of other types of vehicles. Theoretically, an aircraft can be designed to be fabricated entirely from steel just as a ship may be constructed from concrete, however, an all steel aircraft would require a tremendous amount of lift to be produced by the wings. The size of the wings dictated by such a weight would require substantial thrust necessitating larger and more numerous engines, yet again increasing the weight. Thus, for several reasons only a few of which have been elaborated herein, aircraft design strives to produce a strong yet lightweight structure. As suggested, there are other considerations. Corrosion and structural fatigue must be considered as well as rigidity. When all of these factors are balanced, an aluminum structure of equivalent strength, while lighter, is significantly larger than that of steel. Moreover, aluminum is more flexible than steel. Thus, a comparable design in aluminum is constrained by rigidity, not strength.
The solution, with respect to aircraft, was to modify the way in which panels and structures were fashioned. Rather than transferring loads from the surfaces of wings to an internal robust frame, panels were designed to inherently carry and distribute forces such that the internal frame could be minimized. The result was a lightweight, strong and rigid structure that could be carried aloft by the available power sources. However, this solution came at a cost. Even simple aircraft are expensive to design and build, resulting in the cost per mile of delivery of goods by air far exceeding that of land transportation.
Designers of land vehicles are now facing a similar convergence of needs. As fuel becomes scarce, more efficient vehicles are desirable. Environmental concerns have heightened awareness that larger and typically dirtier engines burning more fossil fuels are not the solution. Thus, a trend has existed for several years to make land vehicles lighter, more efficient and powered by alternative fuels and engines. The tasks for which these land vehicles are designed remains essentially the same; that is, land vehicles carry passengers and cargo. Many advances have occurred making the power sources of land vehicles more efficient. Engines operating on fossil fuels have been enhanced to produce the same or more power while utilizing less fuel. Alternative energy sources have been explored including electric and hybrid vehicles. Modifications leading to lighter and stronger frames have lagged in the evolution of land vehicle design. A challenge remains how to design and produce a vehicle frame that is lightweight and strong while being cost effective.
The majority of vehicles today continue to be built around a steel frame. Such a frame is a tradeoff between cost, strength and rigidity. The steel rails in traditional automotive frames must be bent, rolled, cast and custom cut for each new vehicle design. As a result very specific tooling must be designed for each new vehicle. Consequently, there is a monumental cost incurred for changing designs. Thus, the majority of automobile, truck and similar vehicle innovation has focused on lightening upper body components. Little or no attention has been paid to lightening or redesigning the frame of the vehicle. Indeed, many different vehicles possess the same underlying frame. For example, the underlying frame of a Ford F-150 is identical to that of the Ford series SUV's. Similarly, many differing designs of passenger cars are based on the same frame.
The prior art is not without its attempt to use composite structures in automobiles. One such attempt can be found in U.S. Pat. No. 4,573,707 issued to Pabst on Mar. 3, 1986. Pabst discloses a design that attempts to lighten the traditional steel frame using plastic, but falls short of a simplifying design that is easily interchangeable and can be retooled at a minimum cost.
Similarly, an underbody design in U.S. Pat. No. 4,898,419 issued to Kenmochi and Nakamura on Feb. 6, 1990 places honeycomb composite within the passenger floor pan, but does nothing to eliminate the standard automotive frame or change its design to enhance efficiency and ease of manufacturing. Similarly, U.S. Pat. No. 5,849,122 issued to Kenmochi et al. on Dec. 15, 1998 provides for an easier method to incorporate composite sandwich panels into a floor pan but again does not eliminate the need for an exterior frame.
U.S. Pat. No. 4,585,086 issued to Hiramatsu on Apr. 29, 1986 attempts to lighten the frame members using honeycomb composite, but nonetheless maintains the fundamental rail design. The same characteristic approach can be found in the floor panel for a vehicle in U.S. Patent Application Publication 2009/0230729 A1 to Lusk published on Sep. 17, 2009. Here, Lusk specifies a plurality of honeycomb layers that can be used in order to dampen the noise of an interior vehicle compartment. Lusk does not address using such materials in the underlying vehicle frame. Indeed, Lusk specifies that the invention would require an exterior frame adding additional weight and cost to the manufacturing process.
As the ground vehicle industry becomes increasingly more competitive, new applications of materials and structures are sought to lighten vehicles without compromising essential structural integrity. Accordingly, new uses for composites are desirable. A challenge remains for a composite panel design that is both structurally sound to meet strength and rigidity requirements of a land vehicle without having to rely on an external frame. These and other challenges of the prior art are addressed by one or more embodiments of the present invention.